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As petersonra said, for a Div 2 location, both can be used. So both can be treated the same in this situation.

They are not quite identical. For example, "non-incendive" allows currents up to the ignition limit of the atmosphere; "intrinsically safe" only allows current up to 2/3 of the ignition limit.

The reason is that non-incendive is only OK for Div 2 locations, where gas is not routinely present, and so lower risk. Intrinsically safe is allowed in Div 1 areas where gas is continually present, which is a much higher degree of risk. Hence, a safety factor is applied in Div 1 situations.

They both do limit the available energy to prevent ignition, which is why the wiring methods are similar.

I think non-incendive circuits are some of the most misunderstood in Hazardous Area Design. To this day, I have never seen the protection technique used.

I don't think there is a 'technique" as such.

It is a design choice where the equipment is designed under UL guidelines so the risk of creating a spark or high temperature that could ignite flammable gases is low enough that it is considered an acceptable risk. That's why standard relay contacts cannot be used. They might create a spark. Solid state outputs have no such issue.